Coil harness assembly for interventional MRI application

ABSTRACT

A coil assembly for use in MRI imaging includes a harness having a base. First and second arm members extend from a first side of the base and above and over the base and third and fourth arm members extend from a second side of the base and above and over the base. A first cross member extends between the first arm member and the second arm member and a second cross member extends between the third arm member and the fourth arm member. An end of the first arm member is aligned with and detachably connected to an end of the third arm member and an end of the second arm member is aligned with and detachably connected to an end of the fourth arm member. First and second coil members each extend along the harness. The first coil member may be a saddle coil and the second coil member may be a solenoid coil configured to establish a quadrature arrangement.

PRIORITY CLAIM

This application claims the benefit of provisional application Ser. No.60/066,980, filed Nov. 28, 1997.

BACKGROUND

The present invention relates generally to Magnetic Resonance Imaging,and more particularly, to a coil harness assembly for use in MagneticResonance Imaging.

Magnetic Resonance Imaging ("MRI") is a well-known procedure forobtaining detailed, two- and three-dimensional images of a patient basedupon nuclear magnetic resonance ("NMR") principles. MRI is well suitedfor the imaging of soft tissues, and has been used primarily fordiagnosing internal injuries or other medical ailments. A typical MRIsystem will generally include a magnet capable of producing a verystrong homogenous magnetic field, sized to cover or surround a portionof a patient's anatomy; a radio frequency ("RF") transmitter andreceiver system, including a receiver coil which surrounds the portionof the patient's anatomy under study; a magnetic gradient system tolocalize in space a particular portion of the patient's anatomy understudy; and a computer processing/imaging system for receiving thesignals from the receiver coil and for processing the signals intointerpretable data, such as visual images for viewing by the physicianor MRI attendant. Additional information regarding MRI technology andequipment can be found in Van Nostrand's Scientific Encyclopedia, EighthEdition, pp. 2198-2201 and U.S. Department. of Heath and Human Services,"A Primer on Medical Device Interactions with Magnetic Resonance ImagingSystems," Feb. 7, 1997. The general principles and associated equipmentused in MRI is well-known, and as such, additional disclosure is notnecessary.

The advent of "open" MRI systems has provided patients with a morecomfortable examination process and has also provided the MRI attendantsand physicians access to the patient while a portion of that patient isbeing viewed by the MRI system. Examples of such open MR systems are theAIRIS® and AIRIS® II systems, commercially available from HitachiMedical Systems America, Inc. Open MRI systems allow for physicians andother MRI attendants to perform an interventional surgery or othertherapeutic procedures on the patient while the MRI system is producingimages.

Open MRI systems also facilitate "MR Fluoroscopy" which combines nearrealtime signal acquisition, image reconstitution and image display withsuch interventional procedures. Accordingly, by utilizing MRFluoroscopy, the physician will be able to monitor, substantially inreal-time (approximately one image per second), a two- or three-dimensional image of the anatomy while performing a medical procedure onthat anatomy. For example, if the physician wishes to insert an MRcompatible tool, such as a needle or endoscope for example, into aparticular organ, while missing other organs, the physician will be ableto monitor the path of the endoscope, internally, by viewing the MRIimage on a viewing screen.

Conventional coils for use with interventional MRI procedures typicallyinclude single-loop solenoid coil designs. Since these coils are verynarrow (3-5 centimeters in width), the coils are inherently open andallow a large area for patient access. A disadvantage with suchsingle-loop solenoid coils is that the types of interventionalprocedures performed with such a coil is limited. This is because thesingle loop solenoid coils tend to have an undesirable signal to noiseratio; and further, they do not provide a relatively large volume ofcoverage. Accordingly, such a single loop solenoid coil would not bedesired in an interventional procedure where an endoscopic instrumentwill enter into the patient's body at an oblique angle, for example.

Quadrature coil ("QD") arrangements provide a desirable signal to noiseratio. However, a disadvantage of using such QD arrangements ininterventional procedures is that the coil harnesses for housing thecoils and for positioning the coils about the portion of the patientbeing examined often prevent direct access to that portion of thepatient by the physician. For example, a conventional spine/body coilharness for a QD arrangement includes a substantially rectangular basewith an imperforate coil flap extending laterally from each sidethereof. The two flaps wrap about the body of the patient and meet abovethe patient to form a continuous, imperforate loop about the patient.Accordingly, because these flaps substantially enclose the portion ofthe patient's anatomy being examined, interventional access to thisportion of the patient is limited.

Accordingly, there is a need to provide a QD harness that has beenmodified to provide an optimized access to the patient during the MRIviewing process, and in particular, during MR Fluoroscopy.

SUMMARY

The present invention provides a coil harness for a quadrature coilarrangement which substantially optimizes access to the portion of thepatient's anatomy being viewed during the MRI viewing process. In oneaspect of the present invention, the quadrature coil arrangementincludes a two-turn selonoid coil and a saddle coil. The two-turnsolenoid coil is oriented such that the axis of its loops aresubstantially parallel to the patient axis. The saddle coil is orientedsuch that the axis of its loops are substantially perpendicular to thepatient axis. The solenoid coil and the saddle coil are housed within acasing which includes a rectangular base, two pairs of substantiallyparallel, flexible arms extending laterally there from, where each ofthe arms have a coupling mounted to the ends thereof so that the armscan be coupled together to form loops; and a pair of cross bars, eachcross bar extending between a respective pair of parallel arms.

The parallel flexible arms, and the loops formed by coupling the ends ofone pair to another, are axially spaced apart from each other with asubstantially large gap therebetween, which is preferably between 15-25centimeters. Accordingly, the QD coil harness of the present invention,when in an operational state, provides an opening on each side of theharness, each opening extending nearly 150° from the base around theharness between the two flexible arms. These openings provide access tothe patient during MR Fluoroscopy procedures such as spinal procedures,as well as other interventional procedures.

In another aspect of the present invention a coil assembly for use inMRI imaging includes a harness including a base. First and second armmembers extend from a first side of the base and above and over the baseand third and fourth arm members extend from a second side of the baseand above and over the base. A first cross member extends between thefirst arm member and the second arm member and a second cross memberextends between the third arm member and the fourth arm member. An endof the first arm member is aligned with and detachably connected to anend of the third arm member and an end of the second arm member isaligned with and detachably connected to an end of the fourth armmember. First and second coil members each extend along the harness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic representation of the saddle coil of thequadrature coil arrangement provided by one aspect of the presentinvention;

FIG. 2 provides a schematic representation of the solenoid coil of thequadrature coil arrangement;

FIG. 3 provides a perspective view of a harness according to anotheraspect of the present invention with its two pairs of parallel armsconnected in an operational state;

FIG. 4 provides a perspective view of a saddle coil housed within theharness of FIG. 3;

FIG. 5 provides a perspective view of a solenoid coil housed within theharness of FIG. 3;

FIG. 6 provides a perspective view of the harness of FIG. 3 in an openposition;

FIG. 7 provides an enlarged perspective view of one connecting portionof the harness of FIG. 6; and

FIG. 8 provides an enlarged perspective view of another connectingportion of the harness of FIG. 6.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, in one embodiment of the invention a saddlecoil and solenoid coil are utilized. The saddle coil 10 includes a baseor common segment 12 and a pair of wing segments 14a, 14b coupled inparallel to the base segment 12. The two-turn solenoid coil 16 is asingle coil twisted to form two loops 18a, 18b which overlap at point20.

Each of the saddle coil 10 and two-turn solenoid coil 16 include asignal-out port 22, 24, respectively. Each of the coils may include aplurality of capacitors chosen so that the inherent inductance in thecoils is cancelled out by these capacitors. Each of the coils are tunedto the frequency of operation of the MRI system. The frequency ofoperation is defined by the strength of the static magnetic field inunits of Tesla, multiplied by the gyromagnetic ratio, which for protonsis approximately 42.6 MHZ per Tesla. Thus, for the AIRIS system(mentioned above) with its 0.3 T magnet, the frequency of operation isapproximately 12.7 MHz. A coil without capacitors will only haveinductance (and resistance inherent in the conductors). The coil istuned to resonance by using the formula:

    f=1/(2π√(LC))

where L is the inductance of the coil and C is the capacitance of theadded capacitors. Usually, though, more than one capacitor is placed inseries with the coil. Then the total capacitance is calculated as 1/Ctotal=1/C1+1/C2+ . . .

As shown in FIG. 3, coil harness 26 for housing the saddle coil andtwo-turn solenoid coil of the quadrature coil arrangement includes arectangular base 28 having sides and ends respectively. Two opposingpairs of substantially parallel, flexible arms 30a, 30b extend laterallyfrom the sides of the base 28 and generally above and over the base.Each of the arms has a coupling mechanism 32 mounted to the ends thereofso that the opposing, aligned arms can be detachably coupled together toform loops. An axis A of the harness is defined by a line extendingtransverse the ends of the base and extends generally centrally throughthe loops formed by the interconnected arms. A cross bar 34a, 34bextends between each respective pair of arms, and preferably between thecoupling mechanisms 32 of the arms. The coil harness 26 also includeslatch mechanisms 36 for detachably connecting the opposing pairs offlexible arms together during an MRI procedure. A variety of latchmechanisms may be utilized including hook and latch means, straps andplastic buckles or clip connectors, or plastic snap connectors to namejust a few.

Each of the arms are preferably spaced apart from each other with asubstantially large gap there between, which is preferably 15 to 25 cm.When the opposing pairs of flexible arms are coupled together, the crossbars 34a, 34b may be spaced apart from each other as shown to provide agap there between, parallel to the patient or harness axis A, which isabout 50-70 mm. Alternatively, the cross bars 34a, 34b may be positionedadjacent each other providing no significant gap there between.Accordingly, the coil harness 26 of the present invention, when in anoperational state (flexible arms detachably coupled together), providesan opening on each side thereof extending nearly 150° around itscircumference from the side of the base 28 to the cross bar 34a, 34b. Anopening at the top of the patient between the cross bars may also beprovided if desired. It is recognized that the two side openings couldvary depending upon the configuration of the base and positioning of thecross bars, it being preferred that each cross bar be circumferentiallyspaced at least 125° from the closest side portion of the base 28.However, circumferential spacings of less than 125° are considered to bewithin the scope of the present invention.

As shown in FIG. 4, a saddle coil 10 is housed within the harness 26such that the base or common segment 12 extends along the rectangularbase 28 and such that the wing portions 14a, 14b extend separately alonga respective pair of the arms 30a, 30b and into their associated crossbars 34a, 34b. Accordingly, the saddle coil 10 is oriented within theharness 26 such that the axis of its loops (wings) are substantiallyperpendicular to the patient or harness axis A. In more detail, thecommon segment 12 extends along the base 28. Wing segment 14a extendsfrom the common segment 12, along one arm member of pair 30a to andalong the cross bar 34a, and along the other arm member of pair 30a backto the common segment 12. Wing segment 14b extends from the commonsegment 12, along one arm member of pair 30b to and along the cross bar34b, and along the other arm member of pair 30b back to the commonsegment 12.

As shown in FIG. 5, the solenoid coil 16 is housed within the harness 26such that the crossover point 20 resides within the base 28 and suchthat each loop 18a,18b is positioned in a separate harness loop 19a, 19bformed by the opposing, detachably connected flexible arms. As shown inFIGS. 2 and 5, each of the individual loops 18a, 18b are formed by twosegments which are separable, and can be electrically connected togetherat point 38a, 38b. Accordingly, the two-turn solenoid coil 16 isoriented such that the axis of its loops are substantially parallel tothe patient or harness axis A. Two distinct conductive segments 70, 72extend along base 28 for electrically connecting the loops 18a, 18b. Thedistinct conductive segments 70, 72 overlap at point 20 but are not inelectrically conductive contact with each other at such point 20. Thus,a side 74 of loop 18a at one side of the base 28 is electricallyconnected to a side 76 of loop 18b at an opposite side of the base 28 bysegment 70. Similarly, side 78 of loop 18a is electrically connected toside 80 of loop 18b by segment 72.

It will be apparent to those who are skilled in the art that both thesaddle coil 10 and the two-turn solenoid coil 16 are both housed withinthe same coil harness 26, however, they are illustrated separately inFIGS. 4 and 5 for clarity. The harness may be constructed of anysuitable non-ferromagnetic material which is stiff enough to hold thegeneral shape but preferably also flexible enough to allow for somemovement of the arms. For example, a molded plastic or other polymericmaterial could be utilized for the harness skeleton and the coils couldbe run along the surface of the plastic or within channels formed in ormachined into the plastic. The harness skeleton with coils could then becovered with a material such a vinyl to isolate the coils from thepatient. It is recognized that other materials could be utilized for theharness skeleton and the covering.

Referring back to FIG. 3, the base 28, in addition to housing portionsof the saddle coil 10 and two-turn solenoid coil 16, includes othercircuitry necessary for operation of the coils and includes thesignal-out lines 22, 24 which exit the base 28 through cable 40. Asshown in FIGS. 6-8, illustrating the harness 26 in an open position, thesolenoid loops 18a, 18b are coupled together at points 38a, 38b withpositive and negative leads (pin and socket type connectors) 40, 42,respectively. It will be apparent to those of ordinary skill in the artthat there are many other electronic couplings/connectors that aresuitable for the same purpose.

Although the present embodiment is for use as a spine/body coil harness,other embodiments of the invention can be sized for use with differentportions of the patient's anatomy. Additionally, the coils and harnesscan be modified for use in different size patients to optimize thesignal to noise ratio according to the body diameter. Accordingly,although the dimensions specified herein are preferred for a bodyharness, it is recognized that such dimensions may vary widely,particularly where a similar harness is constructed for a smallerportion of anatomy such as an arm or leg. Still further, although armmembers which extend from opposite sides of the base are preferablyaligned and detachably connected to form loops, a coil assembly withingthe scope of the present invention could be constructed with a harnesshaving arm members extending from opposite sides of the base where thearm members connect to each other in a permanent manner or are formedintegral with each other.

It is also recognized and within the scope of the invention that thearms may be substantially rigid, as opposed to flexible. It is furtherwithin the scope of the invention that a four turn solenoid coil replacethe two turn solenoid coil. Such a coil would have two sets of twosolenoid turns. Each set would be positioned close together (2 to 5 cm)within one of the flexible arms while the sets would be spaced apart at15 to 20 cm. Similarly, other coil types and configurations may beestablished using the harness of the present invention.

Referring to FIG. 9, an alternative embodiment of the present inventionis shown in which only one cross member 34' is provided between the pairof arms 30b. Pair of arms 30a connects to the pair of arms 30b in asimilar manner as described previously, except that an additionalelectrical connection is provided at the detachable interface to providea link which completes wing portion 14a of the quadrature coil. Thus,when connected in operable fashion both wing portions 14a and 14binclude a segment which extends along the single cross member 34'. It isalso understood that the single cross member could be formed with acentral opening if desired. Further, two distinct cross members couldlikewise be provided between one set of parallel arms without departingfrom the scope of the present invention.

While the forms and apparatus herein described constitute preferredembodiments of this invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention.

What is claimed is:
 1. An MRI coil assembly comprising:a harnessincluding a base, first and second spaced apart arm members extendingfrom a first side portion of said base and above and over said base,third and fourth spaced apart arm members extending from a second sideportion of said base and above and over said base, a first cross memberextending between said first arm member and said second arm member, anda second cross member extending between said third arm member and saidfourth arm member, wherein said first arm member is aligned with anddetachably connected to said third arm member, and wherein said secondarm member is aligned with and detachably connected to said fourth armmember; a first coil member extending along said harness and including acommon segment extending along said base, a first wing segment extendingfrom said common segment, along said first arm member to and along saidfirst cross member, and along said second arm member back to said commonsegment, and a second wing segment extending from said common segment,along said third arm member to and along said second cross member, andalong said fourth arm member back to said common segment; and a secondcoil member extending along said harness and including at least firstand second loops, said first loop extending generally along said firstarm member and said third arm member and said second loop extendinggenerally along said second arm member and said fourth arm member, saidfirst and second loops being electrically connected.
 2. The MRI coilassembly of claim 1 wherein said first and second arm members extendsubstantially parallel to each other and wherein said third and fourtharm members extend substantially parallel to each other.
 3. The MRI coilassembly of claim 2 wherein said first and second arm members areaxially spaced at least 15 cm from each other and wherein said third andfourth arm members are axially spaced at least 15 cm from each other. 4.The MRI coil assembly of claim 3 wherein said first side portion of saidbase is circumferentially spaced at least 125 degrees from said firstcross member and wherein said second side portion of said base iscircumferentially spaced at least 125 degrees from said second crossmember.
 5. The MRI coil assembly of claim 1 wherein said first andsecond cross members extend substantially parallel to each other.
 6. TheMRI coil assembly of claim 1 wherein said first loop of said second coilmember is formed by a first segment extending along said first armmember and a second segment extending along said third arm member, saidassembly further comprising first and second mating electricalconnectors positioned at respective end portions of said first and thirdarm members for electrically connecting said first and second segments.7. The MRI coil assembly of claim 6 wherein said second loop of saidsecond coil member is formed by a third segment extending along saidsecond arm member and a fourth segment extending along said fourth armmember, said assembly further comprising third and fourth matingelectrical connectors positioned at respective end portions of saidfirst and third arm members for electrically connecting said third andfourth segments.
 8. The MRI coil assembly of claim 1 wherein said firstcoil member comprises a saddle coil and wherein said second coil membercomprises a solenoid coil.
 9. The MRI coil assembly of claim 1 whereineach of said first, second, third, and fourth arm members is flexible.10. The MRI coil assembly of claim 1 wherein said first coil memberincludes an output and said second coil member includes an output, saidMRI coil assembly further comprising at least one conductor operativelyconnected to each of said outputs and extending from said harness. 11.The MRI coil assembly of claim 1 wherein said first and second armmembers extend substantially parallel to each other and wherein saidthird and fourth arm members extend substantially parallel to eachother, and said first and second arm members are axially spaced about15-25 cm from each other and said third and fourth arm members areaxially spaced about 15-25 cm from each other.
 12. A coil assembly foruse in MRI imaging, said coil assembly comprising:a harness including abase, first and second spaced apart arm members extending from a firstside of said base and above and over said base, third and fourth spacedapart arm members extending from a second side of said base and aboveand over said base, a first cross member extending between said firstarm member and said second arm member, and a second cross memberextending between said third arm member and said fourth arm member,wherein an end of said first arm member is aligned with and detachablyconnected to an end of said third arm member, and wherein an end of saidsecond arm member is aligned with and detachably connected to an end ofsaid fourth arm member; a first coil member extending along saidharness; and a second coil member extending along said harness.
 13. AnMRI coil assembly, comprising:a harness including a longitudinal axis, afirst structural loop extending generally orthogonal to saidlongitudinal axis, a second structural loop axially spaced from saidfirst structural loop and extending generally orthogonal to saidlongitudinal axis, at least one cross bar extending generally parallelto said longitudinal axis and between said first and second structuralloops, and a base extending between said first and second structuralloops; a first coil member extending along said harness; and a secondcoil member extending along said harness.
 14. The MRI coil assembly ofclaim 13 wherein said first coil member includes a common segmentextending along said base, a first wing segment extending from saidcommon segment partially along said first structural loop at a firstside thereof to and along said at least one cross bar, and partiallyalong said second structural loop at a first side thereof back to saidcommon segment, and a second wing segment extending from said commonsegment partially along said first structural loop at a second sidethereof to and along said at least one cross bar, and partially alongsaid second structural loop at a second side thereof back to said commonsegment.
 15. The MRI coil assembly of claim 13 wherein said second coilmember comprises a first conductive loop extending along said firststructural loop and a second conductive loop extending along said secondstructural loop, a first side of said first conductive loop at a firstside of said base electrically connected along said base to a secondside of said second conductive loop at a second side of said base, and asecond side of said first conductive loop at said second side of saidbase electrically connected along said base to a first side of saidsecond conductive loop at said first side of said base.
 16. The MRI coilassembly of claim 13 wherein said first coil member is a saddle coil andwherein said second coil member is a solenoid coil including at leasttwo conductive loops, said MRI coil assembly comprising a quadraturecoil assembly.
 17. The MRI coil assembly of claim 13 wherein said firstand second structural loops of said harness are axially spaced about15-25 cm from each other.
 18. The MRI coil assembly of claim 13 whereinsaid first structural loop is formed by first and second aligned anddetachably connected arm members extending from opposite sides of saidbase, and wherein said second structural loop is formed by third andfourth detachably connected arm members extending from opposite sides ofsaid base.
 19. The MRI coil assembly of claim 13 wherein said at leastone cross member comprises a first cross member extending between saidfirst and second structural loops and a second cross member extendingbetween said first and second structural loops.
 20. The MRI coilassembly of claim 13 wherein said first and second structural loops arepositioned toward opposite ends of the harness along its longitudinalaxis providing a spacing between said first and second loops in acentral portion of the harness.